1. Field of the Invention
The present invention relates to methods for transmitting and receiving data in a wireless access system, and more particularly, to methods for efficiently reserving a data channel and apparatuses supporting the same.
2. Discussion of the Related Art
Along with the development of information communication technology, various wireless communication technologies have been developed. Among them, Wireless Local Access Network (WLAN) enables users to connect to the Internet wirelessly through their portable terminals such as Personal Digital Assistants (PDAs), laptop computers, Portable Multimedia Players (PMPs), etc. in homes, offices, or specific service areas.
Since its foundation on February, 1980, the WLAN standardization organization, the Institute of Electrical and Electronics Engineers (IEEE) 802 has been actively working on standardization of WLAN. While WLAN supported 1 to 2 Mbps through frequency hopping, spectrum spreading, infrared communication, etc. in 2.4 GHz according to IEEE 802.11 in the early stage of development, the IEEE 802.11 technology can now support up to 54 Mbps by employing Orthogonal Frequency Division Multiplexing (OFDM).
Besides, the standards of various techniques are under deployment or development in IEEE 802.11, such as Quality of Service (QoS) enhancement, Access Point (AP) protocol compatibility, security enhancement, radio resource measurement, wireless access vehicular environment, fast roaming, mesh networks, interworking with an external network, and wireless network management.
Among the IEEE 802.11 series of standards, IEEE 802.11b supports up to 11 Mbps in the 2.4-GHz frequency band. IEEE 802.11a commercialized after IEEE 802.11b reduces the effects of interference using a 5-Ghz frequency band, instead of the highly congested 2.4-GHz frequency band and increases the communication speed to up to 54 Mbps using OFDM.
However, IEEE 802.11a has the shortcoming of a short communication distance, compared to IEEE 802.11b. Meanwhile, IEEE 802.11g realizes a communication speed of up to 54 Mbps in 2.4 GHz like IEEE 802.11b and satisfies backward compatibility, which attracts much interest to IEEE 802.11g. Furthermore, IEEE 802.11g outperforms IEEE 802.11a in terms of communication distance.
To overcome limits on the communication speed which are a weakness of WLAN, IEEE 802.11n has recently been developed. IEEE 802.11n aims to increase the speed and reliability of a network and extend wireless network coverage. More specifically, IEEE 802.11n is intended to support a High Throughput (HT) of a data processing rate of up to 540 Mbps or higher. To minimize transmission errors and optimize data rate, IEEE 802.11n is based on Multiple Input and Multiple Output (MIMO) using a plurality of antennas at each of a transmitter and a receiver. In addition, IEEE 802.11n may adopt OFDM to increase data rate as well as a coding scheme in which a plurality of redundant copies are transmitted to increase data reliability.
In the IEEE 802.11 standards, the basic access mechanism of the Medium Access Control (MAC) layer is Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) combined with Binary Exponential backofF (BEF).
The CSMA/CA mechanism is robust and variable because it can provide on-demand services and burst data traffic without any central control. Despite these advantages, the CSMA/CA mechanism may cause much time consumption due to data collision, especially much overhead due to a long backoff in a high-speed WLAN environment.
To make the best of the advantage of high-speed transmission performance, Common Control Channel (CCC)-based MAC protocols have been proposed. In these methods, a total bandwidth is divided into a control channel and a data channel. If a source node is to transmit a data frame, the source node may reserve a data channel by exchanging Request To Send (RTS)/Clear To Send (CTS) control frames on the control channel with a destination node. When the RTS/CTS frames are successfully exchanged, the source and destination nodes switch to the data channel and start to process data. Other nodes may continuously attempt to reserve the data channel through the control channel. This RTS/CTS scheme faces some drawbacks. One of the drawbacks is that the control channel requires a large bandwidth because the RTS and CTS frames are not small in size. Another drawback is that while the destination node is processing a data frame, other nodes may not reserve the data channel using RTS/CTS frames. Considering a WLAN-based mode in which most of processes occur to an Access Point (AP) and other nodes, the above drawbacks are very challenging.